Radiator fan issue

[twicebaked]

Hey everyone I’m new here and figured someone on this forum could help me out with my current radiator fan situation.

I drive a 2003 Jeep Wrangler TJ 4cyl

I have replaced the radiator, the fan, replaced the relay and rewired the relay, replaced the thermostat and thermostat housing, and even the radiator cap.

Radiator fan still isn’t coming on, I’ve bypassed the relay and the fan will kick on. It won’t turn on when it reaches operating temp nor when the A/C is on. I’ve checked fuses and they’re good also.

It only passes 200 if I’m idling for too long or stuck in slow moving traffic never goes insanely high though. Been scratching my head trying to figure this out and got nothing, does anyone know what else I could check?

 

[JEEPCJTJ]

How knows, but if the fan isn't coming on because there's something wrong fanwise (is that a word?) the engine would be getting way too hot.

Since it only passes 200 when "idling for too long or stuck in slow moving traffic" I think you got a thermostat that is stuck open and nothing is getting hot enough for the fan to bother fanning.

 

[machoheadgames]

Bad PCM no longer triggering the fan motor relay?

In the mean time you could wire up the fan relay to come on with ignition power so that at least you get proper cooling. Then you can undo that once you get the fix figured out.

 

[twicebaked]

How knows, but if the fan isn't coming on because there's something wrong fanwise (is that a word?) the engine would be getting way too hot.

Since it only passes 200 when "idling for too long or stuck in slow moving traffic" I think you got a thermostat that is stuck open and nothing is getting hot enough for the fan to bother fanning.

I replaced the thermostat and the thermostat housing, is it possible I got unlucky with a faulty thermostat? I know that can happen but isn’t it pretty uncommon

 

[CharlesHS]

Have you checked the A/C condenser for obstructions inside the cooling fins ?
If there are a lot of obstructions; air flow can be restricted which can cause the engine to run warm.

 

[AaronPaul]

Out of the box guess but,
Maybe the PCM is not grounding the relay to turn on the fan.

• Either the PCM itself has an issue, or there’s a wiring problem between the PCM and the relay.
• This could be tested by manually checking for ground at the relay control terminal when the engine reaches temp.
• If there’s no ground signal from the PCM, it may need a reflash or replacement.

• The ECT sensor is unlikely to be the issue because your temp gauge works, meaning the PCM is getting temperature data.
• The PCM controls the ground side of the fan relay—if it fails to do so, the fan won’t turn on.

 

[machoheadgames]

Out of the box guess but,
Maybe the PCM is not grounding the relay to turn on the fan.

• Either the PCM itself has an issue, or there’s a wiring problem between the PCM and the relay.
• This could be tested by manually checking for ground at the relay control terminal when the engine reaches temp.
• If there’s no ground signal from the PCM, it may need a reflash or replacement.
• The ECT sensor is unlikely to be the issue because your temp gauge works, meaning the PCM is getting temperature data.
• The PCM controls the ground side of the fan relay—if it fails to do so, the fan won’t turn on.

This was the same thing I thought, although after looking at the diagram, it seemed that the PCM controls the power side of the relay coil. Either way, I feel like that is probably the issue: PCM not controlling the relay properly.

 

[AaronPaul]

This was the same thing I thought, although after looking at the diagram, it seemed that the PCM controls the power side of the relay coil. Either way, I feel like that is probably the issue: PCM not controlling the relay properly.

It certainly can't

This was the same thing I thought, although after looking at the diagram, it seemed that the PCM controls the power side of the relay coil. Either way, I feel like that is probably the issue: PCM not controlling the relay properly.

The key test would be to ensure that the PCM is providing the 12V signal to activate the relay. If not, focus on the PCM or the wiring.

Since the PCM controls the power side of the relay coil (not the ground), a faulty PCM or relay could still be the culprit, but now we need to focus on ensuring that the relay is getting 12V power from the PCM to activate the fan.